Need advice on possible moisture issue.
 

I have twins and the starboard engine is missing/occasional back fir through carb at 2500+ RPM, (fine below 2500 rpm does not die) Once it warmed up it ran fine (after a few minutes of missing) Did this two mornings in a row and did not do it the rest of the day. Any ideas on moisture in cap, water, seperator or possibly dirty carb?

Thanks!